<!DOCTYPE html>
<html lang="en">

<head>
<meta charset="UTF-8">
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
 <title>Document</title>
<script src="../vue.js"></script>
</head>

<body>
<div id="app">

 <button @click="isHot=!isHot">改变天气</button>
 <h1>今天的天气真{{isHot?"热":"冷"}}</h1>
 <img :src="url" alt="">
</div>
<script>
    Vue.config.productionTip=false;

    const vm =new Vue({
        el:"#app",
        data(){
            return{
                url: "./re.webp",
            }
        },
        //watch配置项
        watch:{
            //监听isHot属性
            isHot:{
                //当被监听的isHot发生改变的时候,handler函数就会执行
                handler(newvalue,oldValue) {
                    console.log("handler",newValue,oldValue);

                    //根据当前的值 去修改url的地址
                    //newValue?this.url="./re.webp" : this.url="./leng.gif"
                    this.url=newValue?"./re.webp" :"./leng.gif"
                }
            }

        }
    })
</script>
 </script>
</body>

</html>